Review articlePerianal fistulas: A review with emphasis on preoperative imaging
Introduction
A fistula-in-ano is an abnormal route of communication between a hole in the lumen of the anus or rectum (internal opening) and a hole in the skin of the perianal region (external opening). A perianal fistula is acquired, and its wall consists of fibrous connective tissue externally and granulomatous tissue intraluminally, with a variable degree of epithelization. The fistulous tract lies between the internal and external opening and may be linear or have a complex course with branches and secondary tracts [1,2].
Fistula-in-ano is a disease known and treated from antiquity. Hippocrates first described fistulotomy and seton placement in patients with perianal fistulas [3,4]. The incidence of the disease nowadays ranges from 1.7 to 2.3 cases per 10,000 persons/year in Europe, with a median age of 40 years. Male to female ratio is 2/1 [[5], [6], [7], [8], [9]]. Lifestyle and past medical history may be associated with an increased risk of the disease. Obesity (BMI>25 kg/m2), high daily salt intake, diabetes, hyperlipidemia, dermatosis, anorectal surgery, smoking, alcohol intake, sedentary lifestyle, excessive intake of spicy/high-fat food, very infrequent participation in sports and prolonged sitting on the toilet for defecation are recognized independent risk factors for perianal fistula formation [10,11].
Pathogenesis in most cases of fistula-in-ano is associated with cryptoglandular infection. In 40%–60% of patients treated for perianal abscess, the healing process leaves a perianal fistula and the disease evolves from acute to chronic phase [[9], [10], [11], [12], [13]]. Other, less common causes of perianal fistulas are anal injuries (traumatic – iatrogenic), Crohn's disease, malignancy of the anal canal or lower rectum, regional irradiation, leukemia or lymphoma, and specific infections (actinomycosis, tuberculosis, lymphogranuloma venereum, human immunodeficiency virus) [1,[9], [10], [11], [12], [13], [14]].
Park's classification is the prevailing system of anatomical classification for fistulas-in-ano [15]. There are 4 types of perianal fistulas according to their relationship to the external anal muscle: Type I or intersphincteric fistulas (45%), Type II or transsphincteric fistulas (30%), Type III or suprasphincteric fistulas (20%), and Type IV or extrasphincteric fistulas (5%) [[14], [15], [16]]. There is also a 5th type of fistula-in-ano described in the literature as superficial or submucosal [12,16,17].
In 1987, Fazio [18] classified perianal fistulas into simple and complex. Simple fistulas-in-ano include submucosal, intersphincteric and low transsphincteric (involving less than 30% of the anal sphincters, when they are not accompanied by secondary fistulous tracts and/or secondary abscess cavities). Complex fistulas-in-ano include high transsphincteric, supralevator, extrasphincteric, horseshoe and fistulas with secondary extensions or abscess cavities. Finally, complex perianal fistulas are considered to be those with high internal opening, non-healing, recurrent, anterior fistulas in women, and those associated with Crohn's disease, malignancy, or co-existing fecal incontinence [12,[16], [17], [18]]. The classification of perianal fistulas into simple and complex was also adopted by Standard Practice Task Force in 2005 [19].
A new classification system of fistulas-in-ano was presented at St James University Hospital in 2000 [20]. This system is based on axial- and coronal-level pelvic magnetic resonance imaging (MRI) findings and describes 5 types of perianal fistulas: Grade I - simple linear intersphincteric fistula; Grade II - intersphincteric fistula with abscess or secondary track; Grade III - transsphincteric fistula; Grade IV - transsphincteric fistula with abscess or secondary track within the ischiorectal fossa; Grade V - supralevator or translevator fistula. Patients with grade I and II fistulas are considered to have simple fistulas with favorable treatment results. Grade III and IV fistulas are considered complex with a potential threatening of continence after surgical treatment (Fig. 1). Grade V fistulas may arise from pelvic inflammatory disease [[20], [21], [22]] (Fig. 2).
The latest classification of perianal fistulas was introduced by Garg in 2017 [23], and it also is based on preoperative pelvic MRI and intraoperative findings: Grade I: low fistula - single tract (intersphincteric or transsphincteric); . Grade II: low fistula – multiple tracts or associated abscess or horseshoe tract (intersphincteric or transsphincteric); Grade III: high fistula – single tract (intersphincteric or transsphincteric) or anterior fistula in female, or associated morbidity (Crohn's disease, fecal incontinence); Grade IV: high fistula – multiple tracts or associated abscess or horseshoe tract (transsphincteric); Grade V: suprasphincteric or supralevator or extrasphincteric. Grade I - II perianal fistulas are considered simple and safe to be treated with fistulotomy. Grade III-V are categorized as complex fistulas and should be treated with a sphincter-sparing surgical procedure [[23], [24], [25]].
The accurate classification and thus knowledge of the topography of a perianal fistula and its relationship to the internal and external anal sphincter before surgery is critical for an effective treatment strategy. The use of diagnostic methods with high sensitivity and specificity in determining the anatomy of a perianal fistula preoperatively is essential [1,19,26,27].
Section snippets
Pelvic MRI
Pelvic MRI with intravenous use of gadolinium was first described in the late 80's and today it is the “gold standard” method for the preoperative imaging of all perianal fistulas, especially the complex ones [16,[28], [29], [30], [31], [32], [33], [34], [35]]. Advantages of MRI include high-contrast imaging of soft tissues, adaptable image field of view and its potential reconstruction in an axial and coronal plane. All these factors contribute to the diagnosis of the fistula-in-ano and the
Conclusions
Preoperative imaging evaluation of patients with perianal fistulas should include pelvic MRI and/or EAUS. Pelvic MRI is associated with statistically significant better results and prognosis after surgical treatment of the disease. Preoperative MRI has led to the discovery of new pathways of extension for perianal sepsis, a new type of complex perianal fistula (RIFIL) and more accurate classification systems for fistula-in-ano (St James classification, Garg classification). EAUS poses high
Financial disclosure
The authors have no funding to disclose.
The author contribution
Study Design: Nikolaos Varsamis, Christoforos Kosmidis, Grigorios Chatzimavroudis, Isaak Kesisoglou, Data Collection: Nikolaos Varsamis, Christoforos Kosmidis, Christoforos Efthymiadis, Fani Apostolidou Kiouti, Ioanna Papathanasiou
Statistical Analysis: Nikolaos Varsamis, Fani Apostolidou Kiouti
Data Interpretation: Nikolaos Varsamis, Christoforos Kosmidis, Grigorios Chatzimavroudis, Konstantinos Sapalidis, Christoforos Efthymiadis, Fani Apostolidou Kiouti, Ioanna Papathanasiou, Paul
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Aristotle University of Thessaloniki, Committee for Bioethics and Ethics approval for PhD research study, ID number: 2454, date: December 7, 2021.
The authors would like to thank Dr. Ioanna Papathanasiou from the Department of Biology, Medical Faculty, School of Health Sciences, University of Thessaly (Larissa, Greece) for providing useful insights that helped improve the study.
References (79)
Anorectal abscess fistula: what do we know?
Surg Clin
(2002)Complex anal fistulae
Gastroenterol Clin N Am
(1987)Comparing existing classifications of fistula-in-ano in 440 operated patients: is it time for a new classification? A Retrospective Cohort Study
Int J Surg
(2017)Assessing validity of existing fistula-in-ano classifications in a cohort of 848 operated and MRI-assessed anal fistula patients - cohort study
Ann Med Surg (Lond)
(2020)- et al.
Current techniques in imaging of fistula in ano: three-dimensional endoanal ultrasound and magnetic resonance imaging
Semin Ultrasound CT MR
(2008) - et al.
Effect of MRI on clinical outcome of recurrent fistula-in-ano
Lancet
(2002 Nov 23) Endoanal ultrasound in perianal fistulas and abscesses. Digestive and liver disease
official journal of the Italian Society of Gastroenterology and the Italian Association for the Study of the Liver
(2006)- et al.
Three-dimensional endoanal ultrasonography in daily proctological practice
Clinics and research in hepatology and gastroenterology
(2011) - et al.
Endoanal ultrasound evaluation of anorectal diseases and disorders: technique, indications, results and limitations
Eur J Radiol
(2007 Mar) - et al.
CT imaging with fistulography for perianal fistula: does it really help the surgeon?
Clin Imag
(2013 Nov-Dec)
A comparison of endoscopic ultrasound, magnetic resonance imaging, and exam under anesthesia for evaluation of Crohn's perianal fistulas
Gastroenterology
Evaluation and management of perianal abscess and anal fistula: SICCR position statement
Tech Coloproctol
Incidence and factors influencing the development of fistula-in-ano after incision and drainage of perianal abscesses
Journal of the Medical Association of Thailand = Chotmaihet thangphaet
Classic articles in colon and rectal surgery
Hippocrates: on fistulae. Diseases of the colon and rectum
The origin of cure for fistula in ano: technique of Hippocrates
Tech Coloproctol
Prevalence of anal fistulas in Europe: systematic literature reviews and population-based database analysis
Adv Ther
An assessment of the incidence of fistula-in-ano in four countries of the European Union
Int J Colorectal Dis
Fistula-in-ano in a defined population. Incidence and epidemiological aspects
Ann Chir Gynaecol
Pathogenesis and treatment of fistula in ano
Br J Surg
Pathogenesis and persistence of cryptoglandular anal fistula: a systematic review
Tech Coloproctol
Risk factors for anal fistula: a case-control study
Tech Coloproctol
Anorectal infection: abscess-fistula
Clin Colon Rectal Surg
Fistula-in-ano
Aust N Z J Surg
Anorectal abscess and fistula-in-ano
J Natl Med Assoc
A classification of fistula-in-ano
Br J Surg
[Focus on the diagnosis and treatment of benign anorectal diseases]
Zhonghua wei chang wai ke za zhi = Chinese journal of gastrointestinal surgery
Evaluation of perianal sepsis: comparison of anal endosonography and magnetic resonance imaging
J Magn Reson Imag : JMRI.
Practice parameters for the treatment of perianal abscess and fistula-in-ano (revised)
Dis Colon Rectum
MR imaging classification of perianal fistulas and its implications for patient management
Radiographics : a review publication of the Radiological Society of North America, Inc.
Our experience with MR imaging of perianal fistulas
Pol J Radiol
MRI evaluation of anal and perianal diseases
Diagn Interventional Radiol
Garg classification for anal fistulas: is it better than existing classifications?—a review
Indian J Surg
Standards Practice Task Force of the American Society of C, et al. Practice parameters for the management of perianal abscess and fistula-in-ano
Dis Colon Rectum
Clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula
Dis Colon Rectum
Magnetic resonance imaging of fistula-in-ano
Dis Colon Rectum
Preoperative MR imaging of anal fistulas: does it really help the surgeon?
Radiology
MRI for assessment of anal fistula
Insights into imaging
Our experience with MR imaging of perianal fistulas
Pol J Radiol
MRI evaluation of anal and perianal diseases
Diagn Interv Radiol
Cited by (7)
Magnetic resonance imaging in the workup of patients with perianal fistulas
2023, Egyptian Journal of Radiology and Nuclear MedicineComparison of MRI and Endoanal Ultrasound in Assessing Intersphincteric, Transsphincteric, and Suprasphincteric Perianal Fistula
2023, Journal of Ultrasound in MedicineClinical value of combined serum MMP-2, MMP-9 and TIMP-1 for the prognosis of perianal fistula patients who received minimally invasive surgery
2023, European Journal of Gastroenterology and HepatologyDiagnostic value of transrectal ultrasound three-dimensional volume imaging in perianal inflammatory diseases
2023, Journal of Chinese PhysicianThe use of ultrasound in colonic and perianal diseases
2023, Current Opinion in Gastroenterology